As conventional in the art, simplex printing includes printing or imaging only a single side of a page or sheet of media. However, duplex printing includes printing or imaging both sides of the page or sheet media. Both simplex and duplex printing are well known in the art of printers, copiers, facsimile devices and the like.
With duplex printing, the alignment of the images on the front and back side of the page is critical. For example, when a stack of pages is folded to make a booklet, the back side of page one will share a margin with the front side of page two. Thus, any misalignment of the front and back images will produce an undesirable visible step at the margin.
Conventional image alignment or registration technologies focus on making the registration or image placement for each side of a page correct so that the front and back images will align correctly. However, to achieve acceptable simplex registration so that the duplexed pages are also acceptably aligned is prohibitively complex and expensive.
In addition, increasing the consistency of the simplex registration to improve the duplex registration can not compensate for small errors in paper size. Since the duplex process flips the page to image the second side, both edges of the page (relative to the media processing direction in the imaging device) are used for positioning the page in the printer. Thus, if the dimension of the paper varies or is incorrect relative to a given size, the front and back side images will be shifted by the amount of the page dimension error. Although a paper dimension error may be small, such small errors in front to back image alignment are very visible.
Accordingly, an object of the present invention is to provide a method and system for duplex image alignment.